Functional electrical stimulation (FES) and a powered exoskeleton are among some of the technologies that aim to restore walking in individuals with paraplegia. FES can be used to obtain desired muscle contractions in the lower limbs through external application of low-level repetitive electrical currents. A powered exoskeleton uses electric motor drives to move the lower-limb joints. Alone, each has limitations. We aim to combine these two technologies to create a hybrid neuroprosthesis that is more advantageous than an FES-based walking system or a powered exoskeleton alone. Because of improved torque reliability, the hybrid walking orthosis can be used for a longer time or over longer distances. Moreover, the use of FES in the hybrid neuroprosthesis may provide therapeutic benefits associated with its use. Specifically, we propose to design and evaluate a new automatic controller for a hybrid walking neuroprosthesis that is composed of an FES system and a semi- powered exoskeleton. Little research has gone into the design and evaluation of control methods for a hybrid walking neuroprosthesis. However, research on its control methods is important for ensuring operational efficiency, gait stability, and torque reliability. In our preliminary results, we show that a model predictive control-based dynamic control allocation can simultaneously control FES and an electric motor to produce a knee extension task, despite the aforementioned challenges. We also show that the new controller can adapt to muscle fatigue in the quadriceps muscle and can sustain knee extension movements for a longer period of time. The proposal's hypothesis is that the new controller can sustain limb movements for a longer period of time compared to a sole FES system and the overall power requirement will be lower than an electric motor system. The specific aims of the proposal are: (1) To physically validate the model predictive control (MPC) method that optimizes the torque contribution from FES and an electric motor in a modified hybrid leg extension machine; and (2) To physically validate the MPC method on a hybrid walking device to elicit walking in persons with spinal cord injury. The proposed project, if successful, will lead to a hybrid walking orthosis that will be lighter and can be used for a longer time or over longer distances. Moreover, the use of FES in the hybrid neuroprosthesis will provide therapeutic benefits; e.g., application of electrical stimulation improved cardiovascular fitness and increased muscle mass and fatigue resistance.